Friction Self-piercing Riveting of AA7075-AA7075-AA6022 in a 3T Configuration Under Varied Manufacturing Conditions

Friction self-piercing riveting (F-SPR) utilizes in-process frictional heat to soften the workpiece, mitigating cracking issues associated with the low ductility of materials at room temperature. A multi-step F-SPR process was developed for an AA7075-AA7075-AA6022 3T configuration, with the thin AA6022 sheet positioned at the bottom—a scenario that challenges the formation of mechanical interlocks in bottom sheet. Process parameters were optimized to control rivet penetration, flaring, and solid-state bonding formation in the bottom sheet. Both solid-state bonding and micro-scale mechanical interlocks were achieved under optimal conditions. For process scale-up, the process was further evaluated under various manufacturing conditions, including variations in workpiece gap, joining access angle, and workpiece thickness. The correlation between these factors and joint performance at different joint interfaces was analyzed using customized lap shear tensile coupon designs. The impact of manufacturing environment variables on peak failure load, absorbed energy, and axial stiffness was thoroughly examined. Additionally, the feasibility of adapting process parameters to accommodate varied manufacturing conditions will be discussed.

This project is funded by the U.S. Department of Energy, Vehicle Technology Offices, under Joining Core Program.